Perpendicular magnetic recording (PMR) has become the mainstream technology for disk drive applications beyond 200 Gbit/in2, replacing longitudinal magnetic recording (LMR) devices. Due to the continuing reduction of transducer size, high moment soft magnetic thin films with a Bs above 22 kG are required for write head applications. A PMR head which combines the features of a single pole writer and a double layered media has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density. In particular, a shielded pole head can provide a large head field gradient at the trailing side due to the presence of a trailing shield and substantially improve the write performance. However, PMR still suffers some problems. One of the biggest issues is the head-induced data erasure that is of particular concern since the erasure occurs after writing. This type of erasure is believed to be caused by a remanent magnetization in the main pole layer and is also related to the sharp pointed geometry of the write pole.
A conventional PMR write head as depicted in FIG. 1 typically has a main pole layer 10 or write pole with a pole tip 10t at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip 10t at the ABS is high enough to switch magnetizations in the recording media 4. A trailing shield 7 is added to improve the field gradient in the down-track direction.
Referring to FIG. 2, a top view is shown of a typical main pole layer 10 that has a large, wide portion called a yoke 10m and a narrow rectangular portion 10p called a pole that extends a neck height (NH) distance y from the ABS plane 5-5 to a plane 3-3 parallel to the ABS where the pole intersects the yoke at the neck 12. The main pole layer 10 flares outward at an angle θ from a dashed line 11 that is an extension of one of the long rectangular sides of the pole 10p. PMR technologies require the pole 10p at the ABS to have a beveled shape (as viewed from the ABS) so that the skew related writing errors can be suppressed.
In the fabrication process, the yoke 10m and pole 10p may be formed by patterning a photoresist layer (not shown) above an alumina layer and then transferring the pattern through the alumina by an etching process to form a mold. An electroplating process or sputter deposition method may be used to deposit a main pole layer 10 that fills the cavity in the alumina. Finally, a lapping process is employed to remove the end of the pole 10p opposite the yoke 10m and thereby define an ABS plane 5-5.
Laminating a write pole layer and main pole is shown to improve the erase-after-write problem by Y. Okada, et al. in “Magnetic properties of FeCo multilayered films for single pole heads”, IEE Trans. Magn., Vol. 40, No. 4, pp. 2368-2370 (July 2004). Anti-ferromagnetic coupling was observed between 25 nm thick FeCo layers and 1 nm thick Cr layers, and [FeCo/Cr]n multilayered configurations helped stabilize the pole.
Slonczewski et al. in “Micromagnetics of laminated permalloy films”, IEEE Trans. on Magn., Vol. 24, No. 3, pp. 2045-2053 (May 1998), report that lamination may be used to eliminate closure-domain walls from certain shapes of practical interest. In one example, two permalloy films each 1.6 microns thick in the main pole layer are separated by a non-magnetic layer that is 12 nm thick.
In other prior art, U.S. Pat. No. 6,950,277 discloses a write pole that has a thin downstream magnetic layer having lower saturation magnetization and a thicker upstream magnetic layer with higher saturation magnetization that is designed to straighten the write field contour of the pole tip.
In U.S. Pat. No. 6,243,939, a first pole layer made of NiFe or CoFeNi is separated from a second pole layer made of the same material by a write gap layer that has a high ion beam etch rate to prevent erosion of the second pole layer during a trimming step.
U.S. Pat. No. 6,233,116 teaches a laminated write pole in which 500 to 600 Angstrom thick layers of high moment magnetic material such as FeRhN are separated by a 100 to 200 Angstrom thick amorphous alloy layer such as CoZrCr. In this case, both types of layers are magnetic to improve overall permeability and uniaxial anisotropy in the high moment material. However, magnetic remanence is not improved.
In U.S. Pat. No. 5,379,172, a magnetic head with upper and lower pole tips having a laminated structure comprised of NiPX alloy layers and NiFe layers is described. The layers on the ends of the lamination have a thickness of D while the middle layers have a thickness of 2D.
U.S. Pat. No. 7,120,988 describes a method of forming a write pole with a trailing shield. The write pole is laminated with magnetic layers (CoFe, NiFe, or CoFe/NiFe) and non-magnetic layers of Rh, Ru, or Cr. There is no description of the relative thickness of the layers but a drawing suggests essentially the same thickness for each laminated layer.
A laminated high moment film involving an antiferromagnetic coupling scheme with Ru coupling layers between high moment layers has been described in U.S. Pat. No. 7,057,853 and by Y. Chen et al. in “High moment materials and fabrication processes for shielded perpendicular write head beyond 200 Gb/in2”, IEEE Trans. Magn. Vol 43, No. 2, p 609 (2007). In the laminated scheme, a high moment material such as a FeCo layer is laminated into several thinner FeCo layers that are separated by non-magnetic layer insertions. When a non-magnetic lamination material such as Ru, Rh, or Cr reaches a certain thickness, a coupling energy is generated such that the magnetization of the FeCo layers on either side of a Ru or non-magnetic layer will align in anti-parallel directions thereby establishing an anti-ferromagnetic (AFC) laminated configuration. Since the magnetization in a FeCo layer is oriented opposite to that of the magnetic moment in the nearest FeCo layer, the remanent magnetization can be reduced.
One disadvantage of prior art AFC lamination schemes is that the coupling strength of a FeCo/Ru/FeCo configuration or the like is typically large and this type of AFC lamination will inevitably cause a large anisotropy field and low magnetic moment under a low field. Although the coupling strength can be lowered by using a thicker non-magnetic layer (increasing Ru thickness from 7.5 to about 18 Angstroms, for example), the magnetic moment will be diluted as the non-magnetic content in the FeCo/Ru/FeCo stack is increased. Therefore, an improved lamination scheme for a write pole is needed that enables a high magnetic moment while simultaneously providing a mechanism to reduce remanence.